Toll-like receptors (TLR receptors or TLRs) represent transmembrane proteins that detect invading pathogens by binding pathogen derived molecules and that induce signaling cascades for proinflammatory gene expression. More precisely, TLRs recognize highly conserved structural motifs known as pathogen-associated microbial patterns (PAMPs), which are exclusively expressed by microbial pathogens, or danger-associated molecular patterns (DAMPs) that are endogenous molecules released from necrotic or dying cells. This includes intracellular proteins such as heat shock proteins as well as protein fragments from the extracellular matrix (McCarthy C. et al, “Toll-like receptors and damage-associated molecular patterns: novel links between inflammation and hypertension” Am. J. Physiol. Heart. Circ. Physiol., 2014, 15 Jan.; 306(2):H184-96).
The TLR receptors were reported as a key component of innate and adaptive immunity (Pasare C., et al (2005) “Toll-Like Receptors: Linking Innate and Adaptive Immunity”. In: Gupta S., Paul W. E., Steinman R. (eds) Mechanisms of Lymphocyte Activation and Immune Regulation X. Advances in Experimental Medicine and Biology, vol 560. Springer, Boston, Mass.).
Among the TLR family, TLR7/8 (toll like receptors 7/8) are nucleotide-sensing TLRs which can be activated by single-stranded RNA (Heil, F. et al, “Species-Specific Recognition of Single-Stranded RNA via Toll-like Receptor 7 and 8.”, Science, 2004, 303 (5663): 1526-29).
Upon PAMP recognition, the TLR typically induces intracellular signaling cascades. An inflammatory response for a short duration can be beneficial because it helps to clear the infectious agent. However, prolonged inflammation is not desirable due to possible tissue damage. Indeed, excessive production of inflammatory cytokines and chemokines via TLR pathways is often associated with many inflammatory-associated and autoimmune diseases. Therefore, fine control of inflammation in the TLR pathway is highly desirable for effective host defense.
The TLR family, and in particular, TLR7/8 plays an important role in pathogen recognition and activation of innate immunity as well as in the regulation of antiviral immunity (Ramirez-Ortiz et al. “TREML4 amplifies TLR7-mediated signaling during antiviral responses and autoimmunity”, Nat Immunol. 2015 May; 16(5): 495-504). Manipulation of TLR7 signaling may be considered as a potential strategy to reduce chronic hyper-immune activation and, thereby, disease progression in HIV infection (S. Baenziger et al “Triggering TLR7 in mice induces immune activation and lymphoid system disruption, resembling HIV-mediated pathology”, Blood 2009 113:377-388).
Other results demonstrated that triggering TLR7 could lead to lymphoid system disruption (Awais et al. 2017; Baenziger et al. 2009). Stimulation of TLRs by the corresponding PAMPs or DAMPs initiates signaling cascades leading to the activation of transcription factors, such as AP-1, NF-κB and interferon regulatory factors (IRFs). IRFs form a family of transcription factors known to play a critical role in antiviral defense, cell growth and immune regulation. More specifically, TLR7 and TLR8 activate IRF5 and IRF7 (Schoenemeyer A. et al. “The Interferon Regulatory Factor, IRF5, Is a Central Mediator of Toll-like Receptor 7 Signaling” 2005, Vol. 280, No. 17, pp. 17005-17012). NF-kappa-B (nuclear factor kappa-light-chain-enhancer of activated B cells) activation by TLR7 is done through MyD88 gene dependent signaling cascade, via their respective TLR domains (Hemmi et al, Nature Immunology, 3(2), 196-200) and TRAF6. This cascade also leads to cytokine secretion and the inflammatory response. NF-κB plays a critical role in the development of tumors in the context of chronic inflammation (J. Cherfils-Vicini et al “Triggering of TLR7 and TLR8 expressed by human lung cancer cells induces cell survival and chemoresistance”, J Clin Invest. 2010; 120(4):1285-1297).
It was shown that TLR7 deficiency leads to TLR8 compensative regulation of immune response (Awais M., et al, “TLR7 Deficiency Leads to TLR8 Compensative Regulation of Immune Response against JEV in Mice”, Frontiers in Immunol., vol. 8, 2017, 160).
In addition to autoimmune diseases, these TLR7/8 are also under investigation in other diseases associated with uncontrolled acute or chronic inflammation, such as malaria (Gao W, et al, “Inhibition of Toll-Like Receptor Signaling as a Promising Therapy for Inflammatory Diseases: A Journey from Molecular to Nano Therapeutics”, Front Physiol. 2017; 8: 508).
The pathology of Alzheimer's disease has an inflammatory component that is characterized by upregulation of proinflammatory cytokines, particularly in response to amyloid-b (Ab), in particular, IL-12 and IL-23 interleukins (Vom Berg J. et al, Inhibition of IL-12/IL-23 signaling reduces Alzheimer's disease-like pathology and cognitive decline, Nat Med. 2012 Dec.; 18(12):1812-9).
It was established that neuroinflammation plays a significant role in Parkinson disease progression. Many studies shown elevated cytokines levels, including TNF and IL-6 in Parkinson disease patients (Pereira JR, IL-6 serum levels are elevated in Parkinson's disease patients with fatigue compared to patients without fatigue, J. Neurolog. Sciences, 2016, 370:153-156).
Although TLR expression was first observed in immune host cells, several reports have described the expression of TLRs in nonmalignant and malignant epithelial cells. In particular, TLR7 and TLR8 are expressed in human lung tumors (Cherfils-Vicini J. et al, Triggering of TLR7 and TLR8 expressed by human lung cancer cells induces cell survival and chemoresistance, J Clin Invest. 2010; 120(4): 1285-1297).
TLRs are expressed on many types of cancer cells. During chronic inflammation, abnormal activation of TLRs in normal fibroblasts and epithelial cells might facilitate neoplastic transformation and carcinogenesis. Cancer cells activated by TLR signals can release cytokines and chemokines that recruit and optimize immune cells to release further cytokines and chemokines. The result is an aberrant cytokine profile associated with immune tolerance, cancer progression and propagation of the tumor microenvironment (Sato Y. et al, “Cancer Cells Expressing Toll-like Receptors and the Tumor” Cancer Microenviron. 2009 September; 2(Suppl 1): 205-214).
Interleukin-6 (IL-6) is one cytokine molecule, which is produced and secreted by various types of cells, including the tumor cells. It is involved in the proliferation and differentiation of malignant cells and found to be high in serum and tumor tissues of most cancers, such as colorectal cancer, breast cancer, ovarian carcinoma, pancreatic cancer, lung cancer, renal cell carcinoma, cervical cancer and multiple myeloma. Elevated levels of IL-6 are associated with aggressive tumor growth and response to therapies in many types of cancer. Patients with high levels of circulating IL-6 are generally associated with poor prognosis and shorter survival, whilst a lower level of IL-6 is associated with better response to therapy. IL-6 plays an important role in tumor progression and therapeutic resistance through inhibition of cancer cell apoptosis and stimulation of tumor-promoting factors, such as proliferation, angiogenesis, etc. These effects are mediated by several signaling pathways (Neeraj Kumari et al, “Role of interleukin-6 in cancer progression and therapeutic resistance”, Tumor Biol. (2016) 37: 11553-11572).
It was demonstrated that p40 monomer of IL-12 plays an important role in helping cancer cells to escape cell death. It was found that different mouse and human cancer cells produced greater levels of p40 than p40 homodimer (p402), IL-12, or IL-23. Similarly, the serum level of p40 was much greater in patients with prostate cancer (Kundu M. et al, “Selective neutralization of IL-12 p40 monomer induces death in prostate cancer cells via IL-12-IFN-γ”, Proc Natl Acad Sci USA. 2017 Oct. 24; 114(43):11482-11487).
Concluding, excessive TLR activation can affect the immune system homeostasis by excessive pro-inflammatory cytokines and chemokines production, and consequently is responsible for the development of many inflammatory and autoimmune diseases, such as systemic lupus, infection-associated sepsis, atherosclerosis, and asthma, and cancer deceases. It is therefore believed that inhibitors/antagonists targeting TLR signals may be beneficial to treat these disorders.
Thus, it is desirable to regulate the pro-inflammatory and anti-inflammatory cytokines and chemokines in the TLR-mediated pathways.
Ligand research can be based on the fact that TLR7 and 8 recognize single-stranded viral RNA. Synthetic analogues have structures reminiscent of DNA or RNA oligonucleotides, such as guanosine-containing compounds and imidazoquinolines with antiviral activities have been described to activate these receptors (Hemmi et al, “Small anti-viral compounds activate immune cells via the TLR7 MyD88-dependent signaling pathway” Nature Immunology, 3(2), 196-200).
Patent application WO/2015/088045 (TAKEDA PHARMACEUTICAL COMPANY LIMITED, JP, 18, Jun. 2015) discloses pyrrolo[3,2-c]pyridine derivatives having a TLR7, TLR9, TLR7/8, TLR7/9 or TLR7/8/9 inhibitory action, which is useful as an agent for the prophylaxis or treatment of autoimmune diseases. But, there still is a need to provide compounds that would effectively inhibit TLR7/8 receptors.
Further, there are drugs targeting TLR7 for different types of indications (S. Rakoff-Nahoum et al. 2009. “Toll-like Receptors and Cancer.” Nature Reviews. Cancer 9 (1): 57-63; Hennessy, Elizabeth J., Andrew E. Parker, and Luke A. J. O'Neill. 2010. “Targeting Toll-like Receptors: Emerging Therapeutics?” Nature Reviews. Drug Discovery 9 (4): 293-307) currently at different stages of development or clinical trials for each of these indications.
Imiquimod (Aldara™; R-837, S-26308), an imidazoquinoline amine, is an immunomodulating agent that was initially approved in 1997 by the FDA for topical treatment of external genital and perianal warts. Studies using imiquimod as a treatment for a variety of benign, premalignant and malignant diseases were researched, such as keratosis, basal cell carcinoma, actinic keratosis, vulvar intraepithelial neoplasia and such autoimmune deceases as localized scleroderma, alopecia (Sauder, D. N. 2003. “Imiquimod: Modes of Action” The British Journal of Dermatology 149 (s66): 5-8). Imiquimod was reported as a Toll-like receptor 7 agonist (Drug News Perspect. 2008 April; 21(3):158-65).
TLR antagonistic trials include treatment of septic shock and autoimmune disorders, in particular systemic lupus erythematosus.
Hydroxychloroquine was reported as a Toll-like receptor 7 antagonist. This drug targets TLR7 for different indications such as rheumatoid arthritis, systemic lupus erythematosus, IGA glomerulonephritis, autoimmune thrombocytopenic purpura, systemic lupus erythematosus, coronary artery disease, prediabetes syndrome, thrombocytopenia and pulmonary sarcoidosis (Scherbel Al., et al. “Comparison of effects of two antimalarial agents, hydroxychloroquine sulfate and chloroquine phosphate, in patients with rheumatoid arthritis”. Cleve. Clin. Q. 1957; 24:98-104; F. Sheikhbahaie et al., “The effect of hydroxychloroquine on glucose control and insulin resistance in the prediabetes condition”, Adv. Biomed. Res. 2016; 5: 145, published online 2016 Aug. 30; Kalia, Sunil, and Jan P. Dutz. 2007. “New Concepts in Antimalarial Use and Mode of Action in Dermatology” Dermatologic Therapy 20 (4): 160-74; A. Makkouk et al “The potential use of toll-like receptor (TLR) agonists and antagonists as prophylactic and/or therapeutic agents”, Immunopharm. and Immunotoxic, 2009; 31(3): 331-338).
However, there are reports of side effects of hydroxychloroquine therapy, such as cardiomyopathy (Catherine A. Millares-Sipin et al, “Restrictive Cardiomyopathy Associated With Long-Term Use of Hydroxychloroquine for Systemic Lupus Erythematosus”, J. of Pharm. Practice. 30(5):571-575, October 2017) while treating lupus erythematosus.
Concluding, modulation of TLR 7/8 receptors allows a treatment to regulate immune system homeostasis, and therefore remains an area of investigation for therapies.
However, the exact mechanism by which modulating these TLRs promotes/inhibits immune responses for different immunity intruding objects remains unclear, and different TLR7/8 modulators have been found to induce different responses. So at present, further research and development of effective and selective TLR7 and 8 modulators may be advantageous.
The major potential drawback to the use of certain TLR antagonists is an increase in susceptibility to infectious agents and tumors.
Moreover, in treating autoimmune deceases, a common problem is a necessity of long term or permanent patient therapy, and therefore it is important to have a variety of medicaments to make it possible to change a medicament as desired or needed in order to avoid unfavorable side effects in the treated subject.
Therefore, the technical problem to be solved by the present invention is to provide a new type of effective TLR 7/8 inhibitor that can be used during treatment of, inter alia, autoimmune deceases, inflammatory diseases and cancer diseases.